【leetcode】Clone Graph

鏈接：https://oj.leetcode.com/problems/clone-graph/

描述:

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.

OJ's undirected graph serialization:

Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbor of the node.

As an example, consider the serialized graph {0,1,2#1,2#2,2}.

The graph has a total of three nodes, and therefore contains three parts as separated by #.

1. First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
2. Second node is labeled as 1. Connect node 1 to node 2.
3. Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.

Visually, the graph looks like the following:

       1
      / \
     /   \
    0 --- 2
         / \
         \_/

方法一：

類似前面Random List copy思路，三遍遍歷，第一遍針對原始的圖中的每一個節點複製一個放在該節點的最後neighbour，第二遍將所有的節點的鄰居修改爲正確的，最後一遍從原來的圖節點剝離新的節點。

超時。

代碼如下：

UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
	if( node == NULL) return NULL;

	UndirectedGraphNode *p = node;
	set<UndirectedGraphNode*> visitNode;
	queue<UndirectedGraphNode*> q;
	q.push(node);
	
	while(!q.empty())
	{
		p = q.front();
		q.pop();
		visitNode.insert(p);
		vector<UndirectedGraphNode*>::iterator it = p->neighbors.begin();
		while( it != p->neighbors.end() )
		{
			if(visitNode.count(*it) <= 0)
				q.push(*it);
			it++;
		}

		UndirectedGraphNode* newNode = new UndirectedGraphNode(p->label);
		newNode->neighbors = p->neighbors;
		p->neighbors.push_back(newNode);
	}

	set<UndirectedGraphNode*>::iterator itSet = visitNode.begin();
	while( itSet != visitNode.end() )
	{
		p = (*itSet)->neighbors.back();
		vector<UndirectedGraphNode*> newNei;
		vector<UndirectedGraphNode*>::iterator itV = p->neighbors.begin();
		while( itV != p->neighbors.end() )
		{
			newNei.push_back((*itV)->neighbors.back());
			itV++;
		}
		p->neighbors = newNei;
		itSet++;
	}

	
	itSet = visitNode.begin();
	UndirectedGraphNode * result = (*itSet)->neighbors.back();
	while( itSet != visitNode.end() )
	{
		(*itSet)->neighbors.pop_back();
		itSet++;
	}

	return result;
}

方法二：

只需要一次遍歷，BFS遍歷，在每次入棧之前對每一個原圖節點新建一個節點，保存新節點和原來節點的關係，在每一次出隊列時對新的節點設置neighbous。

藉助hash加速。

代碼如下：

UndirectedGraphNode* cloneGraphMap(UndirectedGraphNode *node)
{
	if( node == NULL) return NULL;
	map<UndirectedGraphNode*, UndirectedGraphNode*> nodeMap;
	queue<UndirectedGraphNode*> q;
	q.push(node);
	nodeMap[node] = new UndirectedGraphNode(node->label);

	while(!q.empty())
	{
		UndirectedGraphNode *p = q.front();
		q.pop();
		UndirectedGraphNode *copy = nodeMap[p];
		vector<UndirectedGraphNode*>::iterator it = p->neighbors.begin();
		while( it != p->neighbors.end() )
		{
			if( nodeMap.count(*it) <= 0)
			{
				nodeMap[*it] = new UndirectedGraphNode((*it)->label);
				q.push(*it);
			}
			copy->neighbors.push_back(nodeMap[*it]);
			it++;
		}
	}

	return nodeMap[node];
}